[llvm-mca] Instrument assembly code to make multiple code regions

[RKSimon]

Reported here: https://discourse.llvm.org/t/instrument-assembly-code-to-make-multiple-code-regions/67401

It'd be great if it was possible to automatically create mca regions per function/basic-block to make it easier to perform analysis. Either from C/C++ code or IR.

CC @adibiagio

[llvmbot]

@llvm/issue-subscribers-tools-llvm-mca

[adibiagio]

I don’t think it is a good idea to instrument entire functions.
MCA works well for individual basic blocks. However it won’t work for entire functions because branches are not simulated.
The entire function would be interpreted in sequence as if code were contributed by a single basic block.